The invention is a method of making a coated glass substrate. More particularly, the invention is a method of making a coated glass substrate which exhibits low haze.
In producing a coated a glass substrate, it is desired to minimize the amount of haze the coated glass substrate exhibits. In the coating of glass, the crystalline structure of the particular coating contributes to the haze exhibited by the glass. The conventional wisdom is that the larger the crystalline structures contained in each coating applied to a glass substrate, the more haze the coated substrate will exhibit. Thus, previous efforts to minimize the amount of haze have been directed to controlling the rate of crystalline growth of the coating material.
It is known in CVD coating that crystalline growth may be manipulated by controlling the temperature at which a coating is applied. The common wisdom is that the lower the temperature at which the coating is applied, the smaller the size of the resulting crystals contained in the coating applied to the glass substrate. Thus, prior attempts to minimize the haze exhibited by a coated glass substrate have been directed at coating the glass at lower temperatures.
In the case of soda-lime glass, another factor contributing to the haze exhibited by a coated glass substrate is the diffusion of sodium cations contained in the glass that form salts with halogens often associated with the precursors used to form the coatings. The sodium will typically diffuse to the surface of the glass and form a salt at the surface of the glass or in the initial coating layer. Past attempts to minimize the haze associated with the formation of such salts have required the use of precursor materials that do not contain a halogen. These non-halogen containing precursor materials are more expensive than the halogen containing counterparts. Also, the non-halogen containing precursor materials are not as stable as their halogen containing counterparts.
The invention is a method of making a coated glass substrate having a low haze. The invention relates to the discovery that formation of salts on the a surface of the coated glass substrate or an initial coating on the surface of the substrate contributes to the haze exhibited by the coated substrate. In practicing the invention, the relationship between haze exhibited by the coated glass substrate and the formation of salts must be appreciated in view of the relationship between the haze exhibited by the coated glass substrate and the crystalline growth of the coating material.
A soda-lime glass substrate having at least one surface upon which a coating may be deposited is provided. The glass substrate is heated and maintained at a temperature sufficient to volatilize any salts that may be formed during the depositing of a coating directly on the glass substrate. A gaseous precursor mixture including a halogen containing precursor, a metal precursor, an oxidizing agent, and an inert carrier gas is directed toward and along the surface to be coated and reacted at or near the surface of the glass substrate to form a first coating containing a metal oxide coating.
The glass substrate is then cooled to a temperature to reduce crystalline growth in a second coating to be applied over the first coating. A second gaseous precursor mixture including a second metal precursor, an oxidizing agent, and an inert carrier gas is directed toward and along the coated surface of the glass substrate and reacted at or near the coated surface to form a metal containing coating. Subsequently, the glass substrate is cooled to an ambient temperature. The invention also includes a coated glass substrate produced in accordance with the aforementioned method.
The invention may be used to produce a coated glass substrate with a low haze. The invention may be used to produce a coated glass substrate with a haze of less than 2%, preferably less than 1%. The invention may also be used to reduce the cost of producing a coated glass substrate. Through the use of the invention, less expensive halogen containing precursor materials may be used instead of the more costly non-halogen containing substitutes. The use of the halogen containing precursor materials is also beneficial because the halogen containing materials are more stable and easier to manipulate during manufacturing than their non-halogen containing counterparts.